Feat/ Redis HA fix (#283)

* feat: Read Redis Master Ip from app databag

* chore: Improve unit test to include testing for relation data

* chore: Fix linting for noble systems

* chore: Run

* chore: Small refactor

* chore: Add backwards compatibility to Redis relation and its tests

* chore: Refactor

src-docs/charm.py.md

@@ -10,7 +10,6 @@ Charm for Discourse on kubernetes.
 - **DEFAULT_RELATION_NAME**
 - **DATABASE_NAME**
 - **DISCOURSE_PATH**
-- **THROTTLE_LEVELS**
 - **LOG_PATHS**
 - **PROMETHEUS_PORT**
 - **REQUIRED_S3_SETTINGS**

src/charm.py

@@ -390,16 +390,22 @@ def _get_redis_relation_data(self) -> typing.Tuple[str, int]:
         Raises:
             MissingRedisRelationDataError if the some of redis relation data is malformed/missing
         """
-        relation_data = self.redis.relation_data
-        if not relation_data:
+        relation = self.model.get_relation(self.redis.relation_name)
+        if not relation:
             raise MissingRedisRelationDataError("No redis relation data")
+        relation_app_data = relation.data[relation.app]
+        relation_unit_data = self.redis.relation_data
 
         try:
-            redis_hostname = str(relation_data["hostname"])
-            redis_port = int(relation_data["port"])
+            redis_hostname = str(
+                relation_app_data["leader-host"]
+                if relation_app_data.get("leader-host")
+                else relation_unit_data["hostname"]
+            )
+            redis_port = int(relation_unit_data["port"])
         except (KeyError, ValueError) as exc:
             raise MissingRedisRelationDataError(
-                "Wrong hostname or port in Redis relation"
+                "Either 'leader-host' or 'hostname' and 'ports' are mandatory"
             ) from exc
 
         logger.debug(

tests/unit/helpers.py

@@ -109,15 +109,19 @@ def add_postgres_relation(harness):
     )
 
 
-def add_redis_relation(harness, relation_data=None):
+def add_redis_relation(harness, relation_data=None, app_data=None):
     """Add redis relation and relation data to the charm.
 
     Args:
         - A harness instance
 
     Returns: the same harness instance with an added relation
     """
-    redis_relation_id = harness.add_relation("redis", "redis")
+    redis_relation_id = harness.add_relation(
+        "redis",
+        "redis",
+        app_data={"leader-host": "redis-host"} if app_data is None else app_data,
+    )
     harness.add_relation_unit(redis_relation_id, "redis/0")
     # We need to bypass protected access to inject the relation data
     # pylint: disable=protected-access

tests/unit/test_charm.py

@@ -694,46 +694,58 @@ def test_is_database_relation_ready(relation_data, should_be_ready):
 
 
 @pytest.mark.parametrize(
-    "relation_data, should_be_ready",
+    "relation_data, app_data, should_be_ready",
     [
         (
             {"hostname": "redis-host", "port": "1010"},
+            {"leader-host": "redis-host"},
+            True,
+        ),
+        (
+            {"hostname": "redis-host", "port": "1010"},
+            {},
             True,
         ),
         (
             {"hostname": "redis-host", "port": "0"},
+            {"leader-host": ""},
             False,
         ),
         (
             {"hostname": "", "port": "1010"},
+            {"leader-host": ""},
             False,
         ),
         (
             {"hostname": "redis-host"},
+            {},
             False,
         ),
         (
+            {},
             {},
             False,
         ),
         (
             {"port": "6379"},
+            {},
             False,
         ),
         (
             {"hostname": "redis-port"},
+            {},
             False,
         ),
     ],
 )
-def test_is_redis_relation_ready(relation_data, should_be_ready):
+def test_is_redis_relation_ready(relation_data, app_data, should_be_ready):
     """
     arrange: given a deployed discourse charm and some relation data
     act: add the redis relation to the charm
     assert: the charm should wait for some correct relation data
     """
     harness = helpers.start_harness(with_postgres=True, with_redis=False)
-    helpers.add_redis_relation(harness, relation_data)
+    helpers.add_redis_relation(harness, relation_data, app_data)
     assert should_be_ready == harness.charm._are_relations_ready()
 
 

tox.ini

@@ -33,6 +33,7 @@ commands =
 
 [testenv:lint]
 description = Check code against coding style standards
+basepython = py310
 deps =
     black
     boto3